Stabilization of chlorosulphonated polymers by means of salicylalazine



- STABILIZATION or CHLOROSULPHONATED POLYMERS BY MEANS or SALICYLALAZINE George Henry Bowers III, Wilming to"n, DeL, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application June 4, 1953,

Serial N0. 359,654

5 Claims. (Cl. 260-45. 9)

This invention relates to the stabilization of chlorosulphonated polymers, and more especially to the stabilization of chlorosulphonated polymers of the class consisting of polymethylene, polyethylene, and interpolymers ofethylene and vinyl chloride so as to improve their resistance to the action of heat and light aftervulcanizing. f

Chlorosulphonated polymers may be prepared in several ways, notably by the process of the McQueen patent, U. S. 2,212,786. Substances of this sort, having molecular Weights of about 5000 or more, exhibit elastomeric characteristics. Their properties may be enhanced by curing or vulcanizing the raw polymer, somewhat after the manner in which natural rubber is vulcanized, by treatment with suitable curing agents such as, for example, those disclosed in the'McAlevy'et'aL, U. S. Patents 2,416,060 and 2,416,061. These cured products are finding increasing use in a variety of useful applications by virtue of the particular suitability of their unique combination of desirable properties such as strength, resilience, chemical resistance, ozone resistance, etc. In common with many other polymeric materials, however, cured chlorosulphonated polymers have a tendency to undergo change under the influence of continued exposure to heat and light, such change being manifested particularly in the: stress-strain properties of the polymers. and light stabilities of unstabilized chlorosulphonated While the' heat 2,757,163 Patented July 31, 1956 It'is an object of the present invention to provide new compositions of matter comprising chlorosulphonated polymers and a stabilizer therefor. Another object is to provide a method of stabilizing chlorosulphonated polymers. Other objects will appear hereinafter.

According to the present invention it has been found that these and other objects may be accomplished by incorporating into the polymer a minor amount of salicylalazine. Such incorporation may conveniently be carried out by milling the stabilizer into the uncured polymer, al-

' though the precise manner in which the incorporation is aldehyde on hydrazine hydrate in alcoholic solution.

polymers are adequate for many applications, there are;

some existing uses in which an increased degree of stability is desirable, and other potential uses to which it i may be essential, these wherein conditions of exposure to heat and light are likely to be severe.

Stabilizing organic plastic or elastomeric compositions by the addition of appropriate stabilizers is old. However, the nature of the action of such stabilizers is not Well understood, and in the present state of the art, it is impossible 'to predict what efiect'any particular stabilizer ation tests.

will show with a particular plastic or elastomeric substance. The situation is closely analogous to that encountered in the development of catalysts, for chemical reactions, and is, in fact, a situation which for resolution requires the discovery of an anti-catalystsuitable to the special environment where it is to act. For example, numerous stabilizers such as dibasic lead .phthalate, barium ricinoleate, cadmium stearate, and phenyl salicylate, have been developed for use with chlorinated polymers, but have been found entirely inadequate for the stabilization of chlorosulphonated polymers. Aside from differences in the physical character of them'ate'rials, there are distinct differences in the reactions which need to be suppressed in order to bring about stability. Thus, one of the reactions through which chlorosulphonated polymers may deteriorate is via the hydrolysis of an SO OCl group, and that fact renders the problem distinctly different from the stabilization of chlorinated hydrocarbons,

I and (4) accelerator. comprising in general any use. conventional rubber procedure, usually for a total time of performed is not critical for the purposes of this invention so long as a reasonably uniform distribution of the salicylalazine within the polymer mass is efiected prior to final cure.

The salicylalazine employed in the practice of this invention is also sometimes known as salicylaldazine. It is normally a solid, melting in the pure state at about 213 C., and may readily be prepared in a variety of ways well known in the art, as, for example, by the action of salicyl- The invention is more specifically describedand illustrated by means of the following tables and explanatory paragraphs, which, however, are intended solely to exemplify and not to limit the scope of this invention.

" 1 Table I sets forth the compositionof several test batches of chlorosulphonated polythene. As a first step in making up these. compositions, four master batches of elastomeric uncured chlorosulphonated polyethylene were prepared. In this first step, a supply of typical, commercially availableraw polymerxwas fed to the rolls of a conventional water-cooled, two-roll mill of a type commonly used .in the compounding of'rubber, the rolls beingof metal and about 6 inches in diameter, operated at a front roll speed of about 18 R. P. M. and a back roll speed of about 24 R. P. M. so as to provide a friction ratio of about 1.33. The stock was banded for from one to three minutes until a smooth surface and an even bank appeared. Various ingredients representative of the type commonly used in such practice were then added and about 20 minutes until all ingredients were thoroughly blended. The batch was then sheeted off the rolls and set aside. Portions of each of these master batches were cured and used as controls in subsequent stabilizer evalu- Other portions were further compounded and thoroughly blended with the desired amount of finelydivided salicylalazine, generally on a smallermill. having two two-inch diameter metal rolls, each running at the same speed.

Test samples from each of the above compositions were cured via compression molding at about 550 p. s. i. and 1405- 0., using a cure time of approximately 30 minutes. The mold cavities were built up using conventional press-polish plates with appropriate metal spacers. The cavities were lined with aluminum foil coated with a mold-release agent so as to facilitate removing the molded sheet after cure. Press equipment was a laboratory model steam-heated Preco press.

Samples of each of the cured sheets were set aside as controls. Other samples were subjected to rigorous exposure to heat and light under standardized conditions. Finally, standardized tests of stress-strain properties were made on each of the test samples so as to provide comparative data on the initial and final characteritics of both stabilized and unstabilized material;

Heat stability data were obtained on samples'exposed 3"" ..C. in a Precision Scientific Cop circulating air oven. Specimens cut from the cured sheets, with die C of ASTM D-412-41, were hung within the oven in a mannei" similar to that specified in to a temperature of 1 25 TABLE III 1 Comparison of Tri-Mal stocks ASTM 57 8,;. nd' r mov d; aitc ven, da s, h compou d u be 4 5 l o dtoq o otless h bout wo 9 11 b fore being tested. Light stability d ta were Obtained on simi: Parts salicylalazine/IOO chlorosulph ed polyethyypr p redi p m n e h rexp d o 5 hou sl o, 3 3 aWeatherometer inaccordance withASTM;D -'Z5043T initialel ngatiou, per I '595 '620 or exposed seven daystointensive ultraviolet light. The g$g jf f 3 Weatherometeri exposure consisted of intermittently tensile, p. s.i l 2,215 1,900 subjecting thespecimen's to; the action of light having-the gggggg gg f g3 same wave-lengths: as those foundin natural sunlight, but of increased intensity in the ultraviolet range, and p regularlv sprayingwater on the specimens to simulate 1 AB IV the. action of ra1n-. The test 1nvolv1ng seven day exn a "I posure toiultraviolet light-was car-riedout in-a' specially- Campiifisoii'o'f lithizfgfi stbc'ks constructed: boxi fitted-with highintensity; ultravlolet fluorescent lamps, operated at a temperature of 100 E, and 6 7 8 9 my 11 so; placed-1 that samples hung w-1th1n thebox were sublected touniform exposure- Parts'salieylalazinellllo chloro= i The; controls and the;exposed s'ampleS were tested to lg l g lmygt yl 2132? 2 determine their. stress-strain:properties oitensile strength, gfifihfifh 1 1 530 elongationat break, and-stifiness-as" indicated-1n the fol- 2 1 2 8321 913 13 llltraviolflt lowing tallies; Tcjnsile" lQ Q m m tensile,',p.,sz'inlghn'- 2,620 2, 370 2,245 2,000 2,110 1,930 wereztaken according;toa-rnod1fied version of ASTM elpngatlompercenh 530 530 335 p Oven-age7days at C.

D -412,-41. after approprlate condiuomng under controlled tensile s. 1, 330 1, 735 1, 500 2,195 2, 080

temperature and relative humidity The modifications PE Pm F- H 300 in the test procedure were-relatively minor and not here materiaLlsince:allcomparisons'were made amonghsam- 30 ples test'edzin. an identical mannen- A Scott tester (Model TABLE- v- L6 vmanufacturedbyHenryjlJ. Scott and-C0.) wasused v, p 1

for the tensile-and elongation"determinations,operating C a is f bili at aidraw'-rate:of=20 inchesper, mll'llltfi; Stiffness tests, v 1

whereinladez umlzedi A fP g' dorm 1 s'tsbuizi pmoti pairs Ii'iitialTensile/ After-7 days the appl1cat1oni.and release of a umform' bendlng stress ound, ,chlorosulphonated poly- Elongation 1 25O. '1e1 1- tothe: specimen and deterrriinationof the-defiectionuefi -h 999. I l E 5 suiting: For thei urpose .of these evaluations, undesirt 2 1-210 l 1 noazu ablechanges n the measured properties-as the result ,3, 2,13357590 liaaolm of exposure to heatand light are manifested by a deg tsi l fi az ne- 0 creaseinothertensilefand elongatimirvalues; or 'byian ffif f f i T 9 1370/12) crease in the' stiflness :value.'- Theres'ul ts of tests on'each gp rz a g i no e t gggligg Lggg/gq TABLET Contpafis'on of tests'tocks Parts by Mighty oompoundnerflbe r n 1 2 4 5 a 1 i s 9 10 11 12 1s "14 15 Chlorosulphonated polyethylene Hydrogenated Wood Rosin I 2-Meicaptobenzothiazole Cadmium Stearate.

Phenylsalicylaten TABLE II Comparis'on'of magnesia-stocks of salicylala'zine improves each stock in one or both 2) likewise showed better values than the control. parison between compounds 1 and 3 is rendered ditficult inasmuch as it is apparent that the higher centration of stabilizer has retarded the some extent. Nevertheless, it is apparent that the st" bilized sample showed better retention of tensile strength and elongation than did the control.

With the Tri-Mal stocks (Table II), the comparison is again less clear because the salicylalazine has retarded the initial cure. However, it is obvious that after exposure to light, the stabilized stock has increased in tensile strength and retained its elongation, while the control has deteriorated in both respects. Similarly, the control has stiffened much more than the stabilized material.

The litharge stocks (Tables IV and V) are inherently quite stable to the action of light, hence the effect of the added stabilizer is masked by the effect of the litharge in the light exposure comparison. Here the advantage of salicylalazine is shown most clearly in the heat-aging runs, where both the gum stocks and titania-filled stocks containing salicylalazine exhibited significantly higher tensile strength and elongation than did either the corresponding unstabilized controls or the materials stabilized with other candidate stabilizers.

While the examples and preceding discussion have been limited to consideration of chlorosulphonated polyethylene, similar results are obtained with chlorosulphonated polymethylene and chlorosulphonated interpolymers of ethylene and vinyl chloride and these materials may be considered equivalents of chlorosulphonated polyethylene for the practice of this invention.

It will be recognized that the mode of incorporating stabilizer described in the preceding examples, while preferable from the standpoint of convenience in evaluating candidate stabilizers, involves an additional compounding treatment which is desirably eliminated in the preparation of stocks for commercial use. Thus the preferable mode of addition in the latter case comprises adding the stabilizer during the compounding of the other ingredients of the recipe. Preferably the stabilizer is compounded prior to addition of the accelerator, either alone or premixed with one or more of the other ingredients.

The purity and state of subdivision of the salicylalazine is not a critical factor in the practice of the invention. Advantageously, however, the purity of the salicylalazine is such that in the dry state, the compound melts within about 3 C. of 213 C., and the material should be sulficiently line to pass a 20-mesh screen.

Compounding on two-roll mills in which the rolls operate at different speeds has been found to be the most con venient means of effecting uniform distribution of the stabilizer. However, various other compounding techniques such as those conventional in rubber compounding, may be successfully employed.

The amount of stabilizer to be employed will depend largely on the specific use contemplated for the product. Lower amounts will cause less interference with curing time, or a smaller decrease in physical initial properties at standard curing time, but will aiford a lower measure Commore

coninitial cure to of stabilizing action. Depending on the intended application an amount within the range of from about 0.5 to 10 parts of salicylalazine per parts by weight of the chlorosulphonated material, is preferable.

The stabilized products of this invention are especially valuable in applications involving continuous or periodic exposure to elevated temperatures, as for example vehicle tires, conveyor belting, shock mountings, spark plug covers, ignition wire covering, and the like. The stabilized products are also advantageously employed in elastomercoated tarpaulins, weather-stripping, elastomer-based paints, outdoor garden or fire hose, etc., where especial advantage is due to the increased light stability.

As many variations of the present invention are possible, without departing from the teachings herein, it is petitioned that the invention be limited only as indicated in the following claims.

I claim:

1. A composition of matter comprising a chlorosulphonated polymer, having a molecular weight of not less than about 5000, and selected from the group consisting of chlorosulphonated polymethylene, chlorosulphonated polyethylene, and chlorosulphonated interpolymers of ethylene and vinyl chloride, in admixture with from about 0.5 to about 10 per cent, by weight of said chlorosulphonated polymer, of salicylalazine.

2. A stabilized composition of matter comprising a cured chlorosulphonated polymer of the group consisting of chlorosulphonated polymethylene, chlorosulphonated polyethylene, and chlorosulphonated interpolymers of ethylene and vinyl chloride, having a molecular Weight of not less than about 5000, in admixture with from about 0.5 to about 10 percent, by Weight of said polymer, of salicylalazine as a stabilizer therefor.

3. A composition of matter stabilized against the deteriorating action of heat and light comprising a cured, elastomeric, chlorosulphonated polymer of ethylene, in admixture with from about 0.5 to about 10 percent, by Weight of said polymer, of salicylalazine as a stabilizer.

4. A process for stabilizing chlorosulphonated polymers selected from the group consisting of chlorosulphonated polymethylene, chlorosulphonated polyethylene, and chlorosulphonated interpolymer of ethylene and vinyl chloride which comprises adding and intimately admixing salicylalazine as a stabilizer, said polymer having a molecular weight of not less than about 5000, and said salicylalazine being added prior to final curing of said chlorosulphonated polymer, in an amount ranging from about 0.5 to about 10 percent by weight of said chlorosulphonated polymer, and curing the composition.

5. A process for stabilizing chlorosulphonated polyethylene which comprises adding and intimately admixing salicylalazine as a stabilizer, said salicylalazine being added prior to final curing of said chlorosulphonated polyethylene, in an amount ranging from about 0.5 to about 10 percent by weight of said chlorosulphonated polyethylene, and curing the composition.

No references cited. 

1. A COMPOSITION OF MATTER COMPRISING A CHLOROSULPHONATED POLYMER, HAVING A MOLECULAR WEIGHT OF NOT LESS THAN ABOUT 5000, AND SELECTED FROM THE GROUP CONSISTING OF CHLOROSULPHONATED POLYMETHYLENE, CHLOROSULPHONATED POLYETHYLENE, AND CHLOROSULPHONATED INTERPOLYMERS OF ETHYLENE AND VINYL CHLORIDE, IN ADMIXTURE WITH FROM ABOUT 0.5 TO ABOUT 10 PER CENT, BY WEIGHT OF SAID CHLOROSULPHONATED POLYMER, OF SALICYLALAZINE. 